1. Field of the Invention
The disclosed and claimed concept relates to power pole inverters and, more specifically, to an arm assembly wherein insulation encloses a limited number of inverter components.
2. Background Information
Adjustable or variable speed AC drives are commonly used to drive AC induction motors allowing for its speed control. AC drives generally provide the advantage of energy savings because they control the characteristics of its output voltage and current, and thus controlling the motor speed (of the motor they are driving) by the user, optimizing the motor power usage as well as the process it is driving. AC drives operate by taking either incoming AC or DC power, having a fixed frequency and voltage, and converting it to AC power having a voltage or current with variable amplitude and frequency. This allows for the control of the motor speed and power, a requirement in many applications.
An AC drive includes a plurality of inverters and a converter which are electrically coupled through electrical buses and physically coupled through their respective modular bases. The inverters may share a common cooling system connected to the respective heat sinks of each component. That is, an AC drive is made up of a plurality of inverter modules, which are connected to a converter module to create the AC drive, wherein each of the above components is packaged in a relatively small unit having a cooling apparatus. Each of the inverters is made of a modular base, a heat sink or exchanger connected to the base having a plurality of power semiconductor switches, a power supply and a gate driver, thermally coupled thereto, a plurality of capacitors, a plurality of electrical buses connecting the power semiconductor switches to the capacitors, and an insulative medium which encases or covers some or all of the electrically live components, such as the electrical buses. It is further noted that the conductors wrapped around the heat sink. That is, the conductors were U-shaped.
The inverters are, generally, assembled as follows. The semiconductor switches, power supply, gate driver, and other electrical devices, hereinafter “electrical components,” are coupled to the heat sink or base element. The electrical components are coupled to a bus, or a number of electrical buses. The heat sink, number of electrical buses, and electrical components are then disposed in an open ended housing assembly. The housing assembly may abut the heat exchange assembly heat exchanger. Thus, the housing assembly is open on one end and otherwise encloses the heat sink and electrical components. The housing assembly is then filled with an insulative potting compound such as, but not limited to, an RTV silicone based compound, and the potting compound is cured. Thus, the heat sink, number of electrical buses, and electrical components are encased in the potting compound. Alternatively, a minor portion of a component could be exposed. Thus, all, or substantially all, of the components were enclosed. Further, in other embodiments, multiple inverter assemblies were disposed in a single enclosed space that was filled with potting compound.
While this configuration protects the heat sink and electrical components, the potting compound makes repair or replacement of an individual electrical component difficult. Often, the inverter(s) must be sent to the manufacturer as repair/replacement of components cannot be performed on-site.